Fresh-faced, 6-year-old Etan Patz vanished from a SoHo street 20 years ago today, launching one of the city’s greatest unsolved mysteries and galvanizing public awareness of missing kids.

Although no one has been charged in Etan’s disappearance and apparent death, a former federal prosecutor who spent eight years investigating the case believes the prime suspect is Jose Ramos, 54, who is serving 20 years in a Pennsylvania prison for sexually abusing a young boy.

Tragically, Etan disappeared on the first day he convinced his parents he was big enough to walk alone to the bus.

“I believe Etan is no longer with us and that the man responsible for that, Jose Ramos, is behind bars,” said Stuart GraBois, the former Manhattan federal prosecutor who pursued leads as far away as San Diego and Israel.

At the time of Etan’s disappearance, Ramos was:

*A drifter and former mental patient who lived on the Lower East Side and who had a history of trying to lure young boys when he traveled the country.

*An acquaintance of a West Side woman who worked for the Patzes escorting Etan to school during a short-lived school-bus strike in 1979.

*An admitted child molester who later claimed he was with a child resembling Etan on the day the boy vanished.

Despite strong circumstantial evidence against him, Ramos has never been charged in the Patz case. He is eligible for parole in Pennsylvania next year.

Etan’s disappearance and the search by his parents, Stanley, a commercial photographer, and Julie, a school aide, created an outpouring of public concern for missing children.

It led to such highly publicized campaigns as the placement of photos of missing children on the sides of milk cartons.

“It is a legacy to Etan that Ramos is behind bars not harming anyone else, and that innumerable young people have been saved thanks to the awareness his case has generated,” GraBois said.